题目:
1 def add(n,i): 2 return n+i 3 4 def test(): 5 for i in range(4): 6 yield i 7 8 g = test() 9 for n in [1,10,5]: 10 g = (add(n,i) for i in g) 11 12 13 print(list(g))分析:
我们知道生成器函数和生成器表达式都很"懒",只要你不找它取值它就不执行.
函数从上到下开始执行,一直到13行都没开始,13行list()函数找g要值,9-10行的生成器表达式才开始执行,我们将9-10行拆开:
1 n =1 2 g = (add(n,i) for i in g) 3 n =10 4 g = (add(n,i) for i in g) 5 n =5 6 g = (add(n,i) for i in g)根据执行顺序,1-4行都是生成器表达式,在13行找此时6行要值的时候,1-4行都还未执行,我们将表达式都写在6行,得到:
1 n =5 2 g = (add(n,i) for i in (add(n,i) for i in (add(n,i) for i in test())))从里面往外面执行,
test() == (0,1,2,3)
(add(n,i) for i in test()) == (5,6,7,8)
(add(n,i) for i in (add(n,i) for i in test())) ==(10,11,12,13)
(add(n,i) for i in (add(n,i) for i in (add(n,i) for i in test()) )) ==(15,16,17,18)
g=(15,16,17,18)
list(g) == [15,16,17,18]
输出结果:
1 [15, 16, 17, 18]
转载于:https://www.cnblogs.com/shuimohei/p/9686578.html
